Priority is claimed to Japanese Patent Application Number JP2005-192317 filed on Jun. 30, 2005, the disclosure of which is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to a circuit device having a circuit element housed in a case, and a method thereof.
2. Description of the Related Art
Referring to FIGS. 8A and 8B, a configuration of a conventional circuit device 100 will be described. FIG. 8A is a plan view of the circuit device 100, and FIG. 8B is a cross-sectional view thereof This technology is described for instance in Japanese Patent Application Publication No. Hei 11 (1999)-340257.
Referring to FIGS. 8A and 8B, a land 102 made of a conductive material is formed in a center portion of the circuit device 100, and one end of each of a number of leads 101 is disposed close to a periphery of the land 102. The one end of each of the leads 101 is electrically connected to a semiconductor element 104 through a thin metal wire 105, and the other end thereof is exposed from a sealing resin 103. The sealing resin 103 has a function of integrally supporting the semiconductor element 104, the land 102 and the leads 101 by sealing. Moreover, in the case where an optical element is adopted as the semiconductor element 104, a resin having transparency to light is adopted as the sealing resin 103.
Moreover, as a method of sealing a circuit element such as a semiconductor element, there is also a method other than the resin sealing method. For example, there is also a sealing method of forming a circuit device by forming a case having an internal space by use of metal or a resin material and by housing a circuit element in the internal space. This technology is described for instance in Japanese Patent Application Publication No. 2005-26425.
However, in the case where an element emitting or receiving light with a short wavelength is adopted as the semiconductor element 104 described above, there is a problem that the light causes the sealing resin 103 to undergo a color change and the like. Moreover, since the sealing resin 103, in which a release agent or the like is mixed, has insufficient transparency, there is also a problem that light emitted or received by the semiconductor element is attenuated by the sealing resin 103.
Moreover, in a circuit device having a semiconductor element housed in a case, since a space inside the case is hermetically sealed, an air pressure inside the case is changed in accordance with change in an outside temperature. Accordingly, the housed circuit element may be adversely affected. Furthermore, since the space inside the case is hermetically sealed, change in temperature of an outside atmosphere causes moisture condensation inside the case. Thus, there is a problem that the condensed moisture short-circuits an electric circuit in the case.